This invention relates to liquid-liquid extraction columns in which one liquid forms a continuous phase flowing in one direction along the column and the other liquid forms a disperse phase flowing in the opposite direction. The invention is particularly concerned with the type of column in which a packing comprising a series of spaced apart perforated plates is located within the column. One such column is a pulsed column and a typical application is in the solvent extraction of uranium and/or plutonium from an aqueous (nitric acid) phase using tributyl phosphate in odourless kerosene (TBP/OK) as solvent.
A major problem with such columns is the aging of the perforated plate packing over extended periods of operation. Plate aging leads to a drop in column efficiency as a result in variation in the wetting characteristics (contact angle) by the dispersed phase as a result of particles of grease and dirt for example adsorbing onto the plate surface.